The present invention relates to an improvement in a system for adjusting an output current of a discharge electrode for electrophotographic copying machines (hereinafter simply referred to as copying machines).
In the conventional copying machines, the output of a discharge electrode is adjusted to suit for the charging characteristics of a photosensitive member after each replacement of the photosensitive member. Particularly, when the photosensitive member contains a sensitizing agent composed of a selenium compound, the output current must be adjusted after each replacement. When the charging characteristics of the photosensitive member have not been known, the output of the discharge electrode must be adjusted while checking the charging characteristics, requiring a specially designed device. Therefore, it is difficult to quickly perform the adjustment in a site where the copying machine is installed. Or even when the charging characteristics of the photosensitive member have been known, the adjustment must be effected while observing the output current by an ammeter, requiring very clumsy operation and a lot of time.
FIG. 1 is a diagram of a power supply circuit for a discharge electrode incorporating an adjusting circuit, which is used for a conventional copying machine. According to this power supply circuit, constant current characteristics and constant voltage characteristics are obtained by feeding back an output current and an output voltage to an oscillation circuit, relying upon a high-voltage power supply of an inverter type. Namely, with the conventional copying machines, an ammeter is inserted between an output terminal P and a discharge electrode or a voltmeter is inserted between the output terminal P and the ground, and a variable resistor VR inserted in a feedback path to the oscillation circuit is manipulated to vary the output current or the output voltage while viewing the ammeter or the voltmeter to find an optimum output value.